What is it? Truly blue flowers are rare in the garden. This clump-forming salvia (aka gentian sage) from Mexico is dotted with sky-blue, hooded blooms from mid-summer to mid-autumn, and the foliage is aromatic, too. Expect a height and spread of 75cm x 45cm.

Plant it with? For the ultimate blue plant combination, allow the climbing morning glory Ipomoea'Heavenly Blue' to scramble through this salvia; it also looks great with purple-blue Verbena rigida. For a late-summer colour explosion, add yellow dahlias such as 'Clair de Lune' or 'Honka'.

And where? A sheltered spot is of prime importance; full sun or a bit of shade and a free-draining but moist soil will help as well.

Any drawbacks? This plant is a half-hardy perennial: in other words, if you live in an urban heat island with free-draining soil, you can risk leaving it in the soil. Otherwise, lift plants in autumn and store the dahlia-like tubers somewhere frost-free for winter. Alternatively, take cuttings in late summer to provide the next generation of plants.

What else does it do? It's comforting to know that it has the RHS seal of approval, the Award of Garden Merit.